Machine tools, which make an assortment of products including parts for other machines, range from hand-operated machinery capable of shaping or planing metal or wood to modern-day computer-linked systems cabable of building industrial robots.
In connection with the lathe, one of the oldest machine tools, modern improvements include improved cutting materials--such as high-speed steel, stellite, tungsten carbide, and ceramics--which have made faster cutting speeds possible. Faster cutting speeds, in turn, have been the impetus for the development of improved bearing and lubrication systems. Currently, certain lathes are designed with built-in computers programmed to perform preselected functions.
In general, a conventional lathe (or turning machine) will include a headstock portion on which is mounted a face plate, as well as a tailstock portion which is spaced from the headstock portion. An axis of rotation, defined by the headstock and tailstock portions, will be an additional aspect of a conventional lathe or turning machine. The conventional lathe or turning machine will accordingly further include means for holding and rotating a workpiece about this axis. Finally, such a lathe or turning machine will typically further include a tool, means for mounting the tool in fixed relation to the held and rotated workpiece, and means for advancing the tool toward the held and rotated workpiece.
In the normal, long-established manner of peeling wood veneer by rotary cutting, a log (the workpiece) is first selected, then next is supported on a conventional wood veneer-producing lathe in a manner so as to be rotatable about a spindle axis and, finally, is driven by spindles (called "end-dogging spindles") built into the lathe frame. Also provided is a carriage, which may be driven toward the spindle axis at any of several rates of advance per spindle turn, for purposes of achieving a uniform thickness in the veneer. A conventional wood veneer-producing lathe carriage, in this regard, is typically further equipped with a full-length cutting knife as well as with a separately-controlled pressure bar (also called nose bar).
See, for example, an article entitled "Peeling Veneer With a Floating Bar: Effect of Bar Pressure on Veneer Quality," authored by O. Feihl and M. N. Carroll, the article appearing in the December 1973 issue of Forest Products Journal (Vol. 23, No. 12), at pages 28-31.
The pressure bar (or nose bar) is designed to contact the wood at a point immediately above the cutting edge of the knife. To produce veneer of maximum quality, those who practice this technology conventionally manually select a fixed mechanical setting, for maintaining a preselected spacing (called "horizontal gap") from the knife, to produce veneer having a thickness which is slightly less than the desired veneer thickness, the purpose being to compress the wood slightly, resulting in a cleaner cut, which is a desirable effect.
See, for example, a paper entitled "Thickness Variation in Veneer Peeled With a Floating Bar," authored by O. Feihl and M. N. Carroll, the paper (dated 1973) presented (as Report OPX62E) at Eastern Forest Products Laboratory (800 Montreal Road, Ottawa, Canada K1A OW5).
A second purpose, or desired effect, is to provide a stabilizing pressure against the wood (also called block), and also to dampen vibration, to reduce chatter, and to minimize random movement, all of which are desired effects. Alternatively, conventionally employed is a hydraulic servo-head system (referred to herein as a hydraulic servo head), comprising a servo-connected hydraulic cylinder, which, for purposes of accomplishing the above-noted desired effects, responds to an electronic position command to maintain its desired gap setting.
In any event, a gap will initially be selected by those skilled in the art, and the initial gap value subsequently changed, to accommodate the nature and physical properties of the wood.
If all trees had a common, homogeneous compositional make-up and structure, and were of exactly the same wood type and density, the above would be a very simple and tidy solution to the manufacture of veneer products having uniform product thickness and quality.
However, all trees are not equal and, as a result, wood density characteristics will vary from one block to the next. It is generally recognized that such variations may be influenced, in a minor way, by temperature. In this regard, I believe that such variations are even more influenced by such environmental tree-growth considerations as frequency and/or periods of drought or excessive rain (and attendant annual growth-ring spacing), presence or absence of knots, frequency and degree of insect infestation, and so forth.
Gap value selection is thus affected by such wood physical characteristics as tree-growth environment and history, wood species and variety, wood temperature, and wood density.
Normal block pre-conditioning typically calls for a temperature of approximately 140.degree. F. (about 60.degree. C.) for the wood.
Because wood temperature is one of the more readily apparent indicators relating to wood hardness (or density), some attempts have been made, by those skilled in this particular art, to adjust pressure bar (also called "nose bar") gap, in a manner so as to relate this gap value to wood temperature. However, such variations are often made merely in arbitrary fixed increment, generally relating only to temperature, without regard for such wood physical properties as wood density. As a result, such selection criteria have not proven generally reliable on production scale, resulting in the abandonment of such selection criteria in many cases.